Promote SELECT to fast opcode (89) - used in every print statement

SELECT was previously SLOWOP_SELECT (20) but is actually hot path code
called once for every print/say statement to get the default filehandle.

Performance impact:
- Eliminates SLOW_OP dispatch overhead
- Reduces bytecode size by 1 byte per print statement
- Improves CPU i-cache utilization

Dense opcodes now: 0-89 (no gaps, maintains tableswitch optimization)

Author: fglock

src/main/java/org/perlonjava/interpreter/BytecodeCompiler.java

@@ -816,8 +816,9 @@ public void visit(OperatorNode node) {
             }
         } else if (op.equals("select")) {
             // select FILEHANDLE or select()
-            // Call IOOperator.select() which handles the logic
-            // For now, emit a SLOW_OP that will call the operator at runtime
+            // SELECT is a fast opcode (used in every print statement)
+            // Format: [SELECT] [rd] [rs_list]
+            // Effect: rd = IOOperator.select(registers[rs_list], SCALAR)
 
             int rd = allocateRegister();
 
@@ -827,9 +828,8 @@ public void visit(OperatorNode node) {
                 node.operand.accept(this);
                 int listReg = lastResultReg;
 
-                // Emit SLOW_OP with SLOWOP_SELECT
-                emitWithToken(Opcodes.SLOW_OP, node.getIndex());
-                emit(Opcodes.SLOWOP_SELECT);
+                // Emit SELECT opcode
+                emitWithToken(Opcodes.SELECT, node.getIndex());
                 emit(rd);
                 emit(listReg);
             } else {
@@ -840,9 +840,8 @@ public void visit(OperatorNode node) {
                 emit(listReg);
                 emit(0); // count = 0
 
-                // Emit SLOW_OP with SLOWOP_SELECT
-                emitWithToken(Opcodes.SLOW_OP, node.getIndex());
-                emit(Opcodes.SLOWOP_SELECT);
+                // Emit SELECT opcode
+                emitWithToken(Opcodes.SELECT, node.getIndex());
                 emit(rd);
                 emit(listReg);
             }

src/main/java/org/perlonjava/interpreter/BytecodeInterpreter.java

@@ -849,6 +849,17 @@ public static RuntimeList execute(InterpretedCode code, RuntimeArray args, int c
                         break;
                     }
 
+                    case Opcodes.SELECT: {
+                        // Select default output filehandle: rd = IOOperator.select(list, SCALAR)
+                        int rd = bytecode[pc++] & 0xFF;
+                        int listReg = bytecode[pc++] & 0xFF;
+
+                        RuntimeList list = (RuntimeList) registers[listReg];
+                        RuntimeScalar result = org.perlonjava.operators.IOOperator.select(list, RuntimeContextType.SCALAR);
+                        registers[rd] = result;
+                        break;
+                    }
+
                     // =================================================================
                     // SLOW OPERATIONS
                     // =================================================================

src/main/java/org/perlonjava/interpreter/InterpretedCode.java

@@ -366,6 +366,11 @@ public String disassemble() {
                     sb.append("JOIN r").append(rd).append(" = join(r").append(separatorReg)
                       .append(", r").append(listReg).append(")\n");
                     break;
+                case Opcodes.SELECT:
+                    rd = bytecode[pc++] & 0xFF;
+                    listReg = bytecode[pc++] & 0xFF;
+                    sb.append("SELECT r").append(rd).append(" = select(r").append(listReg).append(")\n");
+                    break;
                 case Opcodes.SLOW_OP: {
                     int slowOpId = bytecode[pc++] & 0xFF;
                     String opName = SlowOpcodeHandler.getSlowOpName(slowOpId);

src/main/java/org/perlonjava/interpreter/Opcodes.java

@@ -376,6 +376,13 @@ public class Opcodes {
     /** Join list elements with separator: rd = join(rs_separator, rs_list) */
     public static final byte JOIN = 88;
 
+    // =================================================================
+    // I/O OPERATIONS (89)
+    // =================================================================
+
+    /** Select default output filehandle: rd = IOOperator.select(rs_list, SCALAR) */
+    public static final byte SELECT = 89;
+
     // =================================================================
     // SLOW OPERATIONS (87) - Single opcode for rarely-used operations
     // =================================================================